'The view, the food, the waitress setting the food down, her family – they could all go away. She was going to engage with the world that wasn’t there.' Photograph: Billy Farrell/bfanyc.com/Rex

It’s a scene so commonplace that it’s hardly worth specifying the details. But it was on Wednesday night, in a restaurant in Mousehole in Cornwall. Next to us was a family of four, with two adult children. The daughter, in her mid-20s, was gazing down beneath the table at her lap, glowing blue, periodically stabbing at it. The view, the food, the waitress setting the food down, her family – they could all go away. She was going to engage with the world that wasn’t there, condensed and switch off-able.

Simon Schama issued a heartfelt and sympathetic plea last week, which he must know sounded like Canute facing the waves with pretend dignity. Opening the new displays at the National Portrait Gallery, he reflected on the habit of looking outwards that created art in the first place, and regretted that we now seem to be in an age that looks downwards, or inwards. The exchange of looks, he said, citing Hogarth, is the “foundation of human interaction”. To observe what is there is the only place that art, thought, literature can start from.

It about your preferred distance from the human race, Those who text at dinner like relations to be conducted remotely

It’s fair to say that, now that pretty well everyone owns a mobile phone, your engagement with the world can be judged by where your phone is while you’re eating dinner. The woman in the Mousehole restaurant had yielded to a heartfelt request, I would say, in placing it in her lap under the table. More usual will be those who place it on the table beside the plate; and now, there are those who eat with one hand, the other holding the iPhone 6, rapt, quite oblivious of the poor waiter trying to pour your water.

To me, it seems fairly staggeringly rude to behave like this when you’re in company, but nobody else seems to feel that way. The truth of the matter is that if present company were instantly removed, and replaced by the people who are currently receiving messages, the phones wouldn’t be put away. The messaging would probably continue, to another set of people. It isn’t about showing that you’d prefer to be talking to people who aren’t in the room. It’s about your preferred distance from the human race. Those who text at the dinner table would generally like their relations with humanity to be conducted at electronic speed, remotely.

Of course, none of this is going to lead to art, or literature, or intelligent observation about our fellow human beings. Schama is right that the creative intelligence, as well as our existence as sociable beings, rests on the exchange of glances. The art of the past is the consequence of the indecently penetrating gaze. Look at Goya’s sketches of old women now on show at the Courtauld Institute, and you can see that sometimes he just stopped in the street and stared at a most interesting sight. Reports of the behaviour of great novelists often stresses their penetrating and rather disconcerting inspection – Ivy Compton-Burnett was said to look people up and down in a detail that was barely decent.

The perceived indecency of the act of staring has led to its being policed and controlled

Probably, in an age where most people are withdrawn in public, gazing downwards, it is scandalous to possess the outward gaze that writers and artists must develop. It often shocks or terrifies a class of would-be writers when I give them an exercise in observation – to transcribe an overheard conversation, or to describe a complete stranger’s clothes, gait or resting expression. In some ways, the practice of observation is experiencing a golden age since, like the woman in Mousehole, the targets are so absorbed that they don’t notice you staring for long minutes. But the perceived indecency of the act of staring has led to its being policed and controlled. I’m always being told to “move on” by security staff when I’m just looking at the interesting sight of a shoplifter being wrestled to the ground. Once, at Exeter University, where I was supposed to be teaching writing, I found myself being reprimanded by an angry head of faculty. I had been discovered transcribing the interesting speech patterns of a colleague in a dull faculty meeting.

It isn’t universal, and travellers often discover cultures where it’s quite normal still to gaze with civil interest at each other. And I don’t believe that it’s irreversible. In Japan, it’s universally accepted as unacceptably rude to make a phone call when on public transport. It would be nice if people understood, not just the rudeness of preferring your phone to the physical presence of your friends, but how stupid it makes the phone-wielder look. In a room of people gazing down, or wielding their phone as an intermediary, the conspicuous intelligence, the obviously interesting presence is the face looking upwards and outwards, with curiosity; the best company is the one that meets a frank, flirtatious gaze with another one.